Selection of bearings
Function of bearings:
Support the loads exerted on the
shaft
Locate the shaft in position
Radially
Axially
Type of bearings:
Sliding contact bearings
Rolling contact bearings
Sliding contact
bearings
W W
Hydraulic oil
Hydrodynamic Hydrostatic
bearings bearings
Rolling contact
bearings:
Ball bearings
Single row ball bearing
Double row ball bearing
Self alignment ball bearing
Angular contact ball bearing
Thrust ball bearing
Roller contact bearings
Taper roller bearing
Straight roller bearing
Conical roller bearing
Concave roller bearing
Thrust roller bearing
Needle bearings
Ball bearing
Roller bearing
Spherical roller
thrust bearing
Radial tapered
roller bearing Ball
thrust Roller thrust
bearing bearing
Classification of bearing load
The loading on bearings can
be classified into three
groups:
Solely radial loading
Solely axial loading
Combined radial and axial
loading
The Bearing
series
Extra Light Medium Heavy
light
Standardisation of ball
bearings :
Series Designation
6309
Light : 200
Medium: 300Bearing type Bore diameter
Heavy : 400 Series number
Main parts of a typical ball
bearing
Ball Ball retainer
Inner ring
Outer ring
Selection of ball
bearings:
The bearing must be of the series best
suited to the installation, in regard to both:
capacity and
dimensions.
The type of bearing selected must be
suitable for the type of imposed load,
radial,
thrust or
combined.
The size of the bearing must be such as to
give the required length of service with
sufficient assurance.
Selection of ball
bearing
Bearings have to resist some combination
of radial and thrust loads.
Combined load must be reduced to an
equivalent radial load
In general the equivalent load Fe may be
computed by the equation:
Fe XFr YFa
X Y Type of bearing
1 1.5 Deep groove
0.5 1 Angular contact
0.5 2.5 Self aligning
Selection of ball
bearing
Experiments have shown that the
life of a ball bearing is a function of
the load it carries.
Cd
. Ln =
Fe
( ) 3
Cd: dynamic specific capacity of bearing.
Ln: Life of bearing in millions of revolution.
Fe : Equivalent load
The above equation can be rewritten as
1/ 3
Cd = Fe Ln
Bearing life
Life in working
Class of machine hours
1
Instruments and apparatus that are used only seldom. Demonstration apparatus,
mechanisms for operating sliding doors
2 Aircraft engines 1000 - 2000
Machines used for short periods or intermittently and whose brake down would not
3 have serious consequences; hand tools, lifting tackles in workshops, hand operated 4000 - 8000
machines, generally agricultural machines, cranes in erecting shops, domestic machines
Machines working intermittently and where breakdown would have serious
4 consequences. Auxiliary machines in power stations, conveyor plant for flow 8000 - 12000
production, lifts cranes for piece goods; machine tools used infrequently
5
Machine for use 8 hours per day and fully utilized: stationary electric motors, general 12000 - 20000
purpose gear units.
6
Machine for use 8 hours per day and fully utilized: machines for engineering industry 20000 - 30000
generally: cranes for bulk goods, ventilating fans, countershafts
Machines for continuous use 24 hours per day: Separators, compressors, pumps, mine
7 hoist, stationary electric machines, machines in continuous operations on board naval 40000 - 60000
ships
Machines required to work with high degree of reliability 24 hours per day: pulp and
8 paper machinery; public power plants, mine pumps, pumps in water works, machinery 100000 - 200000
in continuous operation on board merchant ships
Factor of safety
Safety
factor, life
Safety factor, life of 5 to 10 years
of 10 to 20 Load
years conditions
Continuous Continuous 10 hours per day Intermittent
3 2 1.5 0.5 ----- 1 Steady load
4 3 2.5 1 ------- 2 Light shock
5 4 3.5 2 ------- 3 Moderate
shock
6 5 4.5 3-------- 4 Severe shock
Over-all dimensions of radial ball
Bore of inner race (d) Outside diameter D mm Width B (mm)
bearings
SAE
Bearing 200 300 400 200 300 400
Number mm in
series series series series series series
00 10 0.3937 30 35 9 11
01 12 0.4724 32 37 10 12
02 15 0.5906 35 42 11 13
03 17 0.6693 40 47 62 12 14 17
04 20 0.7874 47 52 72 14 15 19
05 25 0.9843 52 62 80 15 17 21
06 30 1.1811 62 72 90 16 19 23
07 35 1.3780 72 80 100 17 21 25
08 40 1.5748 80 90 110 18 23 27
09 45 1.7717 85 100 120 19 25 29
10 50 1.9685 90 110 130 20 27 31
11 55 2.1654 100 120 140 21 29 33
12 60 2.3622 110 130 150 22 31 35
13 65 2.5591 120 140 160 23 33 37
14 70 2.7559 125 150 180 24 35 42
15 75 2.9528 130 160 190 25 37 45
16 80 3.1496 140 170 200 26 39 48
Installation of ball
bearings:
The shaft must be designed to
take the inner ring (race)., see
fig. (6.7)
A suitable mounting must be
designed for the outer ring
(race).
Lubrication must be provided
for the bearing
Methods of sealing the
lubricant and preventing
penetration of foreign matter
Fastening ball bearing to a shaft
Example2
A shaft is supported by two bearings. One of the
bearings carries a radial load of 1200 lb and an axial
load of 600 lb with minor shocks. The shaft runs at
230 rpm and operates 10 hours per day for 5 days per
week. Select a suitable ball bearing with a service life
of 2 years if the diameter of the shaft can be varied
between 31615and
312
inch.
Fr = 1200 lb
Fa = 500 lb
Minor shock
Speed = 230 rpm
Operating hours =10/day
Working days = 5/week
Years = 2
SELECT FACTOR OF SAFETY
Factor of safety = 2.5
Safety
Fe = XFr+ Yfa
factor, life
of 10=to1.5
20 X 1200 + 1 X 600
Safety factor, life of 5 to 10 years
Load
= 2100 lb
years conditions
Service life (Ln)
X Y Type of bearing
Continuous Continuous 10 hours per day Intermittent
1 1.5 Deep groove
Ln 3= 2 1.5 0.5 ----- 1 Steady load
0.5 1 Angular contact
4 3 2.5 1 ------- 2 Light shock
0.5 2.5 Self aligning
5 4 3.5 2 ------- 3 Moderate
shock
6 5 4.5 3-------- 4 Severe shock
15 <d<3
316
1
inch
2
101.01<d<88.9 mm
From tables
Select deep grove ball bearing
SAE219 with dynamic capacity 17600
Bore diameter = 95 mm
Dissassebly
Assembly
Manufacturing
Thank You
